Posted by benny (68.78.128.91) on October 03, 2008 at 08:28:02:
In Reply to: Delamination of Anodize on 2024 Alloy posted by Mike Roberg on October 01, 2008 at 08:06:57:
: We are processing parts for our customer that we have done for many years. These parts are made from 2024. The parts are very large blocks that weigh close to 80 lbs. We process 2024 everyday for many customers and only have this problem with this particular job. After Anodize and the parts are in the packaging area ready to be unracked we do a tape test on the parts to check for adhesion of the coating per our customers request. Sometimes we will see massive failure where all the black dye comes off(not the anodize itself) with the tape and maybe not every part on the workbar. This part gets DA sanded before we recieve it in house for Anodize and arrives to us with a very thin film of aluminum dust from the sanding. This dust is very fine and is very hard to remove. We have speculated that this delamination is due to cleaning or the lack of not removing all the loose material from the surface as we prep the part for Anodize. I have been working on this problem for several months and I keep coming back to this. We run similar parts for other customers but don't have the delamination problem with thier parts, even if the the parts have been DA sanded. It seems that the sanding method is being done different and the dust is not as fine with other work. Also the problem goes away for a few months and arises again at a later date. I can't help but think that there is a surface condition on the alumimun that we are not able to make into and anodize friendly situation. We have tried longer etch times to try to undercut the problem but it is not the magic bullet. I guess my biggest question is this. Is the tape test a relevant test in the industry or are we subjecting these parts to a test that is not relevant? The 2nd question is after stripping and replating the parts, and the parts are alway good, no delamination, could I conclude that this is a surface situtation on the part that is somewhat a moving target that doesn't fall into our process?
No tape test is not a standard practice for anodize. For paint adhesion, a crosshatch is cut into the coating and tape used to see if the little squares come off.
But you basically answered your own question when rework fixes the parts. Stripping removes all contaminants and your finish is good. Longer etch on a 2000 series part is usually an accident waiting to happen. Have you ever tried going straight into the anodize tank with these parts, allow them to anodize for 5-10 minutes, then rinse them and go back to the etch tank? It kinda saves time of anodizing, dying and sealing before stripping. The anodize tank will throw off all the dust and grit so the etch tank can take off the light coating and problem areas in one shot.